Former Trump national security adviser Michael Flynn leaves federal court in Washington, Friday, Dec. 1, 2017. Flynn pleaded guilty Friday to making false statements to the FBI, the first Trump White House official to make a guilty plea so far in a wide-ranging investigation led by special counsel Robert Mueller.

The first member of President Donald Trump's White House has been charged with and pleaded guilty to a crime stemming from interactions with Russia. And depending upon whom you ask, Michael Flynn's plea deal either signals doom for the Trump administration or is a good sign about the lack of a case being pieced together by special counsel Robert Mueller.

Mostly, though, the plea deal leaves plenty of big, open questions that will determine which side of that debate is right. Below are four of them.

1. What does Flynn even know?

There is no question more central to this debate — and, right now, to the entire Russia investigation. Whether you think the plea deal was appropriate, a good deal or a bad deal, the most significant thing about it is that it signals Flynn is cooperating. And it's likely his cooperation is far-reaching.

"The plea is significant not so much for itself, but for its value as an investigative tool," said Jack Sharman, who served as special counsel to the House Financial Services Committee during the Whitewater investigation of President Bill Clinton. "The special counsel now has an ally who understands that he will only get a benefit if he 'cooperates' with the investigation and that the meaning of 'cooperation' is entirely within the control of the prosecutors."

Sharman added that "to have value for the pleading defendant, his or her cooperation needs to be robust — no half-measures [on] anything."

It's clear Flynn was on his heels here, as The Post's Carol D. Leonnig reported Friday night. And liberals are currently fantasizing that Flynn is spilling all kinds of secrets about potential collusion with Russia and God-knows-what-else. But he can only share that information if he has it.

Trump undoubtedly had a personal affinity for Flynn and seemed to trust him implicitly. But to suggest Flynn knew something incriminating is to believe that there was something incriminating at all and that Flynn was party to it. And depending upon whom you ask, the light charges Flynn pleaded to Friday might signal that there simply wasn't much there.

Here's how the National Review's Andrew McCarthy put it:

"Understand: If Flynn's conversations with the Russian ambassador had evinced the existence of a quid pro quo collusion arrangement — that the Trump administration would ease or eliminate sanctions on Russia as a payback for Russia's cyberespionage against the Hillary Clinton campaign and the Democratic Party — it would have been completely appropriate, even urgently necessary, for the Obama Justice Department to investigate Flynn," McCarthy wrote. "But if that had happened, Mueller would not be permitting Flynn to settle the case with a single count of lying to FBI agents. Instead, we would be looking at a major conspiracy indictment, and Flynn would be made to plead to far more serious offenses if he wanted a deal — cooperation in exchange for sentencing leniency."

To the contrary, for all the furor, we have a small-potatoes plea in Flynn's case.

2. Why did Flynn lie?

McCarthy's argument absorbed, it still begs the question: Why did Flynn feel the need to misrepresent his conversations with the Russian ambassador? Generally when talking to the FBI, you'll want to be extremely careful about what you say, for fear of exactly the kind of pickle in which Flynn finds himself.

Was he simply worried about violating the Logan Act, a seldom-used federal law against conducting diplomacy if you aren't authorized to do so? Or were Flynn's lies merely the latest in a long volume of those close to Trump seeming to cover up the existence and substance of their contacts with Russia?

It's no secret Flynn misstated details of these contacts — that much we knew dating back to February — but why wouldn't he have been more careful? Was it because he just messed up and didn't fully process the question, or did he actually have something to hide? It's difficult to believe one would lie for no good reason, given the stakes, and yet here we are — again.

3. Who else, besides Jared Kushner, directed Flynn to talk to Russia?

According to The Post's reporting, Flynn contacted the Russian ambassador with the knowledge and at the direction of plenty of influential people.

". . . Court records and people familiar with the contacts indicated [Flynn] was acting in consultation with senior Trump transition officials, including President Trump's son-in-law, Jared Kushner, in his dealings with the diplomat," according to a Washington Post report. "Flynn's plea revealed that he was in touch with senior Trump transition officials before and after his communications with the ambassador."

Kushner has been named by reporters, but court documents indicate there were more people involved. And there simply weren't that many people senior to Flynn on the transition team.

The biggest question of all would seem to be whether one of the officials is Trump himself.

4. Why did Flynn direct Russia not to respond to U.S. sanctions?

One of the things to which Flynn pleaded guilty was lying about asking Russia not to respond to the Obama administration's recently announced sanctions in response to Russian interference in the 2016 election:

"In another conversation, on Dec. 29, Flynn called the ambassador to ask Russia not to escalate an ongoing feud over sanctions imposed by the Obama administration, court records say. The ambassador later called back and said Russia had chosen not to retaliate, the records say," according to a Washington Post report.

There is plenty left out about these conversations. Perhaps the biggest is why Flynn argued that Russia shouldn't escalate the feud over sanctions and why Russia granted his request. Did he simply make a suggestion and not explain why, or did he indicate that the Trump administration might seek to ease those sanctions when it took over less than a month later?

That's been a central question for the better part of a year. And it remains so even after Flynn's plea deal.